I am trying to make a seamless repeat in AI in CS4.

Normally I make a box (with no fill or stroke) around it to make the repeat and then drag it into the swatch box. My problem is that if it the box isnt exact it will leave white border around it and the sides will not match.

Is there anyway or function on CS 4 that allos me to not have to do this? Just automatically generate a perfect staggered design repeat ?